Membrane separation of organics from aqueous solutions

ABSTRACT

Organics are separated from aqueous solutions by contacting the aqueous solution feed with a first surface of a polymeric membrane selectively permeable to organic components; while maintaining a second and opposite membrane surface at a lower chemical potential than the first membrane surface for said organic components, permeating a portion of the organic components into and through the membrane; and withdrawing from the second membrane surface a mixture having a higher total concentration of organic components than the organic components concentration of the aqueous solution feed stream.

This is a division of application Ser. No. 636,400, l filed Dec. 1,1975, now U.S. Pat. No. 4,218,312.

BACKGROUND OF THE INVENTION

The invention relates to the membrane separation of organics fromaqueous solutions. In another aspect the invention relates tohydrophobic polymeric membrane separation of organic components fromaqueous solution feedstreams. Yet in another aspect the inventionrelates to a process for the hydrophobic, polymeric membrane separationof organic components from aqueous solution feedstreams in combinationwith a solution sink which provides the lower chemical potential on thepermeate side of the membrane. Still another aspect of the inventionrelates to a process for the removal of environmental contaminants suchas organic components from waste water streams.

The separation of organic components from aqueous mixtures such asdispersions, emulsions, solutions, and the like has been accomplished byvarious means, for example, distillation, filtration, solvent extractionand a combination of these and other methods. However, these methodsoften fail to provide satisfactory separation of the organic componentsfrom the aqueous solutions without the utilization of multiple unitapparatus or the high energy input required by phase change techniques.Solvent extraction methods frequently result in exchange of one solutionof organics for another thus presenting the continuing need for theseparation of organic components from aqueous solutions. Because of thedisadvantage of the existing method for the separation of organiccomponents from aqueous solutions, a simple, inexpensive processadaptable for all types of aqueous solutions is highly desirable.

Membrane separation techniques have been utilized to separate mixturesof two or more different molecules, for example, aqueous mixtures, mixedhydrocarbons, azeotropic mixtures, and the like. However, knownseparation techniques utilized in the separation of aqueous mixturesfrequently are followed by secondary procedures such as distillation.Because of the disadvantage of the existing separation methods whichprincipally involve a substantial energy input of a thermal, chemical,or mechanical nature, a simple membrane separation for separatingneutral organic components from aqueous solutions is needed.

The growing need for additional sources of water from salt water or fromcontaminated sources has directed intensive investigations into theseparation of water from aqueous mixtures. Substantial improvements havebeen made in known water separation procedures based on flashevaporation, membrane separation, electrodialytic action, freezing andthe like. However, paralleling such needs for additional sources ofwater is the need for improved recovery procedures concerning organiccomponents contained in aqueous waste streams. In order to achieve aninexpensive separation of organic components from aqueous solutions,techniques must be developed which require minimum equipment and energyinput.

Accordingly an object of this invention is to provide the separation oforganic components from aqueous streams utilizing hydrophobic polymericmembrane systems. Another object of this invention is to providehydrophobic membrane pervaporization, liquid-liquid dialysis, or gas togas separation of organic components from aqueous solutions wherein theprocess is as quantitative as possible.

SUMMARY OF THE INVENTION

It has been discovered in accordance with the present invention thatneutral organic components are effectively separated from aqueoussolutions through polymeric membranes which are selectively permeable tothe neutral organic components. The effective separation system utilizesa lower chemical potential on the permeate side of the membrane than onthe feed side of the membrane through chemical and/or physical means.One essential feature of the invention requires that the polymericmembrane be hydrophobic and selectively permeable to the neutral organiccomponents of the aqueous solution. The process according to theinvention separates neutral organic components from aqueous solutionsthrough the steps of (a) contacting an aqueous solution of neutralorganics feed stream with a first surface of a hydrophobic, polymericmembrane permeable to the neutral organic components; (b) maintaining asecond and opposite membrane surface at a lower chemical potential thanthe first membrane surface for said neutral organic components; (c)permeating a portion of the neutral organic components into and throughthe membrane; and (d) withdrawing at the second membrane surface amixture having a higher total concentration of neutral organiccomponents than in the aqueous solution feed stream. The lower chemicalpotential on the permeate side of the membrane can be maintained byvacuum conditions or at least a pressure differential whenpervaporization or gas to gas separation systems are required; howeverwhen liquid to liquid dialysis systems are required, an optional featureof the invention is the utilization of a solution sink such as chemicalmeans for maintaining the lower chemical potential. The solution sinkcan be selected from potential solvents for the neutral organiccomponents and/or complexing solutions.

DETAILED DESCRIPTION OF THE INVENTION

The process of the instant invention comprises utilization ofhydrophobic, polymeric membranes which are selectively permeable toneutral organic components contained in aqueous solutions and which aresubstantially impermeable to other components of an aqueous solution, ormaterials utilized in the solution sink such as complexing solutions orsolvents for the neutral organic components which are in contact withthe membrane. The process according to the invention can utilize neutralorganic component solvent complexing solution, or vacuum vapor mode onthe permeate side of the membrane for maintaining the lower chemicalpotential which is an essential feature of the invention. The lowerchemical potential provides a force which drives the neutral organicspermeate through the selective, hydrophobic polymeric membrane, and canresult from the solution sink solvent, complexing solution, or vaporvacuum mode having capacity for neutral organics permeate. Multi-stageoperations are feasible as scale-up utilization of the invention sinceindividual stages permit various concentrations and temperatures inorder to achieve optimum driving forces.

Continuous processing according to the invention is achievable whereinan aqueous solution feedstream containing neutral organic components ispassed on one side and in contact with a hydrophobic, polymeric membranehaving selectivity for the neutral organic components, while a solutionsink or vapor vacuum is in contact with the permeate side of themembrane. The lower chemical potential of, for example, the neutralorganic component solution sink together with counter currentrelationship of the neutral organic aqueous solution feedstream,provides driving force for permeating neutral organics through theseselective membranes into the neutral organic solution sink. The neutralorganic enriched solution sink or vapor can be swept or moved byphysical means to suitable processing which promotes the recycling ofthe solvents or complexing solutions.

For each individual stage the effectiveness of the separation is shownby the separation factor (S.F.). The separation factor (S.F.) is definedas the ratio of the concentration of two substances, A and B, to beseparated, divided into the ratio of the concentrations of thecorresponding substances in the permeate ##EQU1## where C_(a) and C_(b)are the concentration of the preferentially permeable component and anyother component of the mixture or the sum of other componentsrespectively.

In the pervaporization or vapor vacuum embodiment of the invention, thefirst or feed side of the membrane is usually under a positive pressure,while the second side is under a negative pressure, relative toatmospheric pressure. Another preferred mode of the pervaporizationseparation is where the second side of the membrane is maintained at avacuum of 0.2 mm to about 759 mm of mercury.

The term "chemical potential" is employed herein as described by Olaf A.Hougen and K. M. Watson ("Chemical Process Principles, Part II," JohnWiley, New York, 1947). The term is related to the escaping tendency ofa substance from any particular phase. For an ideal vapor or gas, thisescaping tendency is equal to the partial pressure so that it variesgreatly with changes in the total pressure. For a liquid, change inescaping tendency as a function of total pressure is small. The escapingtendency of a liquid always depends upon the temperature andconcentration. In the present invention the feed substance is typicallya liquid solution and the permeate side of the membrane is maintainedsuch that a vapor or liquid phase exists. A vapor feed may be employedwhen the mixture to be separated is available in that form from anindustrial process or when heat economies are to be effected inmulti-stage.

In one embodiment of this inventive process, the first or feed surfaceof the hydrophobic, polymeric membrane is contacted with an aqueoussolution containing neutral organic components in the liquid phase,while the second surface of the membrane is contacted with a neutralorganic solvent or complexing agent solution. However, the aqueoussolution feedstream can be in the vapor phase wherein it is preferablethat the feed side of the membrane be under positive pressure inrelationship to the permeate side. In order for permeation of theneutral organic components to occur, there must be a chemical potentialgradient between the two zones, i.e. the feed side of the membrane ascompared to the permeate side of the membrane. The chemical potentialgradient for the purposes of this invention requires a chemicalpotential of the feed zone be higher than the chemical potential in thepermeate zone. Under such conditions a portion of the neutral organicsin the aqueous solution feedstream will dissolve within the membrane andpermeate therethrough since an essential feature of the invention isthat the hydrophobic, polymeric membrane be selectively permeable to theneutral organic components of the aqueous solution.

The permeation step according to the invention is conducted bycontacting the neutral organic aqueous solution feedstream in either theliquid or vapor phase with the hydrophobic, polymeric membrane andrecovering a neutral organics enriched permeate fraction from the otherside of the membrane. The permeate can be either in the form of aneutral organics vapor, solution, or complexing solution of the neutralorganics. To facilitate rapid permeation of the neutral organics, thechemical potential of the permeated neutral organics at the surface ofthe membrane from the permeate side can be kept at a relatively lowlevel through the rapid removal of the permeate fraction, for example,through a continuous process wherein the neutral organics enrichedvapor, solution, or complex solution is continuously removed andreplaced by a vacuum or non-enriched neutral organic solvent and/orcomplexing agent.

The term "solution sink" for the purposes of this invention defines aliquid sweep utilized on the permeate side of the membrane and isinclusive of both selective solvents for neutral organic components andsolutions of neutral organic component complexing agents, or both.Suitable selective solvents for neutral organics used as solution sinkcan be selected from solvents which permit the total concentration ofthe neutral organic to be greater on the permeate side than on the feedor permeant side of the membrane. The term "neutral organics" for thepurpose of this invention will be defined as those organics which haveneither acid or basic characteristics. "Organic compounds" being definedas those compounds which generally consist of carbon and hydrogen withor without oxygen, or other elements, except those in which carbon playsno important part, e.g., carbonates; therefore the term "neutral organiccomponents" is defined as those components or compounds which generallyconsist of carbon and hydrogen, with or without oxygen, nitrogen, orother elements except those in which carbon plays no important part, andwhich are characterized as neither acid nor basic.

Hydrophobic, polymeric membranes as used in the inventive process arenon-porous, that is free from holes and tears and the like, whichdestroy the continuity of the membrane surface. Useful hydrophobicmembranes according to the invention are comprised of polymericmaterials. The membranes are preferably as thin as possible whilepermitting sufficient strength and stability for use in the permeationprocess. Generally separation membranes from about 0.1 to about 15 milsor somewhat more are utilized according to the invention. High rates ofpermeation can be obtained by the use of thinner membranes which can besupported with structures such as fine mesh wire, screens, porousmetals, porous polymers, and ceramic materials. The hydrophobic membranemay be a simple disk or a sheet of the membrane substance which issuitably mounted in a duct or pipe or mounted in a plate or frame filterpress. Other forms of membrane may also be employed such as hollow tubesor fibers through or around which the feed is applied or is recirculatedwith the permeate being removed from the other side of the tube as aneutral organics enriched sweep solution, complex or enriched gasstream. There are other useful shapes and sizes which are adaptable tocommercial installations, which are in accordance with the invention.The polymeric membrane compositions may be linear, cross-linked,grafted, and vary over a wide range of molecular weights. Also suitableaccording to the invention are copolymers and polymeric blends. Thehydrophobic membranes, of course, must be stable and insoluble in theaqueous feed solution and the various sweep liquid solvents andcomplexing agents. Membrane insolubility as used herein is taken toinclude that the membrane material is not substantially soluble orsufficiently weakened by its presence in the sweep solvent or aqueousfeed solution to impart rubbery characteristics which can cause creep orrupture resulting from conditions of use, including use pressure. Thehydrophobic membranes may be polymers which have been polymerized ortreated so that specific end groups are present in the polymericmaterial. The hydrophobic membranes utilized according to the inventiveprocess may be prepared by any suitable means such as, for example,casting of film or spinning of hollow fibers from a "dope" containingpolymer in solvent. Such preparations are well-known in the art. Animportant control of the separation capacity of particular hydrophobic,polymeric membrane is exercised by the method used to form and solidifythe membrane, e.g., casting from a melt into control atmosphere orsolution and various concentrations and temperatures. The art ofmembrane use is known with substantial literature being available onmembrane support, fluid flow and the like. The present invention ispracticed with such conventional apparatus. The membrane must of course,be sufficiently thin to permit permeation as desired but sufficientlythick so as not to rupture under operating conditions. The membraneaccording to the invention must be selectively permeable to the neutralorganic components contained in the aqueous solution in comparison tothe other components of the aqueous solution feedstream and the take-upsolutions and complexing agents on the permeate side of the membranewhen utilized.

The following exemplary hydrophobic polymeric membranes are suitableaccording to the process of the invention and are selectively permeableto neutral organics contained in aqueous solution:

Polyolefins such as polybutadiene, polyethylene, polyisoprene, andcopolymers thereof such as copolymers ethylene and vinylacetate,ethylene and acrylic acid, and the like; fluorinated polyolefins such aspolyvinylfluoride, polyvinylidenefluoride, and copolymers such aspolyvinylidenefluoride and polyvinylpyrrolidone, ethylene andtetrafluoroethylene, fluorinated ethylene and polyethylene and the like;silicone polymers and resins such as methyl silicone polymeric resin,methyl/phenyl silicone resin, and the like; polyurethanes; and undercertain specified conditions aliphatic nylons.

The aqueous solution containing the neutral organic components may becontinuously or intermittently introduced into the hydrophobic,polymeric feed zone. The permeated neutral organics are removed from theopposite side of the membrane in batch or continuous manner through theuse of various sweep forms, vapor, complexing solutions or solvent sink.The rate of introduction of the aqueous solvent feedstream and theremoval of the permeate fraction may be adjusted to provide the desiredproportions of permeate and permeant fraction. A number of permeationstages may be employed where the permeate and permeant fractions may berecycled to various stages. In each permeation zone the membrane may beused in the form of sheets, tubes, hollow fibers, or other structureswhich preferentially provide a maximum amount of membrane surface whileutilizing a minimum volume of space.

The absolute pressure of the feed and the permeant zones may varyconsiderably. Pressures range from a few millimeters of mercury to ashigh as 500 to 1,000 psig or higher according to the invention dependingupon the strength of the membrane and the separation requirement, i.e.,a vapor or a liquid system or a combination liquid vapor system. Whenthe permeate zone is under the liquid phase conditions, pressure isgenerally not an important factor. However, when gas or vapor feedmixtures or pervaporization conditions are utilized, higher pressures onthe feed zone can result in greater chemical potential and is desirable.

The membrane permeation step is preferably operated under conditions oftemperature which can vary over a wide range from about -20° C. to about200° C. or more depending upon the neutral organic components ofinterest, aqueous solutions, solution sink, or pervaporization mode andthe thermal condition of the aqueous solution. Higher operatingtemperatures are frequently desirable because of the increased rates ofpermeation; however, the present invention is also concerned with energyinput efficiency and minimum temperature change for the purpose ofseparating neutral organics from aqueous solutions.

To illustrate further the present invention and the advantages obtainedtherefrom, the following examples are given without limiting theinvention thereto. It is also possible that many changes in the detailscan be made without departing from the spirit of the invention.

EXAMPLES 1-14

Neutral organic components were removed from aqueous solutions utilizingmembranes which are selectively permeable to the organics under liquidto gas separation conditions. The following Table 1 presents the resultsachieved according to specific embodiments of the invention includingseparating methanol, ethanol, butanol, ethylbenzene, acetonitrile, andacrylonitrile through olefinic polymeric membranes. These olefinicpolymeric membranes include copolymers as well as blends wherein thecopolymers or blends were substantially comprised by weight of thepolymeric olefins. Examples 1-14 utilize in combination with thehydrophobic olefinic polymeric membranes, a chemical potential gradientresulting from pervaporization conditions. Conditions such as feedconcentration, temperature, rate, and separation factor for the variousmembranes and neutral organic components are presented in the followingTable 1.

                                      TABLE 1                                     __________________________________________________________________________    Pervaporization (<0.1 mm Hg on permeate side and 1 atmosphere on the feed     side)                                                                                                               Membrane                                                                            Separation                        Example                Temperature                                                                          Rate (grams/hr                                                                        thickness                                                                           Factor                            Number                                                                             Membrane Feed     °C.                                                                           -11 cm.sup.2)                                                                         (mils)                                                                              (water/organic)                   __________________________________________________________________________    1    Poly (butadiene)                                                                       50% by wt                                                                     methanol 25     0.007   6     0.33                              2    Poly (butadiene)                                                                       50% by wt                                                                     ethanol  25     0.01    6     0.35                              3    Poly (ethylene)                                                                        50% by wt                                                                     ethanol  70     0.017   2     0.80                              4    Poly (ethylene)                                                                        7% by wt                                                                      butanol  70     0.020   2     0.073                             5    Poly (butadiene)                                                                       7% by wt                                                                      butanol  25     0.014   6     0.020                             6    Copoly (ethylene/                                                             vinyl acetate)                                                                         7% by wt                                                             (65% by wt                                                                             butanol  70     0.056   4     0.028                                  ethylene)                                                                7    Copoly (ethylene/                                                             vinyl acetate)                                                                         7% by wt                                                             (88% by wt                                                                             butanol  70     0.035   5     0.023                                  ethylene)                                                                8    Poly (ethylene)                                                                        5% by wt                                                                      acrylonitrile                                                                 0.1% by wt                                                                             50     0.0199  2     0.105                                           acetonitrile                                                                  0.002% by wt                                                                  propionitrile                                                   9    Copoly (ethylene/                                                             acrylic acid)                                                                          5% by wt                                                             (97% - molar                                                                           acrylonitrile                                                        ethylene)                                                                              0.1% by wt                                                                    acetonitrile                                                                           50     0.0036  4     0.081                                           0.002% by wt                                                                  propionitrile                                                   10   Copoly (ethylene/                                                             vinyl acetate)                                                                         5% by wt                                                             (65% by wt                                                                             acrylonitrile                                                        ethylene)                                                                              0.1% by wt                                                                    acetonitrile                                                                           50     0.089   4     0.049                                           0.002% by wt                                                                  propionitrile                                                   11   Poly (isoprene)                                                                        50% by wt aceto-                                                              nitrile  50     0.0310  11    0.107                             12   Poly (ethylene)                                                                        50% by wt aceto-                                                              nitrile  50     0.029   1     0.13                              13   Poly (ethylene)                                                                        150 ppm ethyl-                                                                benzene  20     --      1     <10.sup.-3                        14   Poly (ethylene)                                                                        100 ppm ethyl-                                                                benzene  70     --      1     <10.sup.-3                        __________________________________________________________________________

EXAMPLE 15

A neutral organic component (ethanol) was removed from aqueous solutionutilizing a copolymer membrane comprised of 65% by weight ethylenepolymer and 35% by weight vinylacetate polymer. A feedstream comprisedof 90% by weight ethanol/10% by weight water was contacted with a 3 milthick membrane for a period of 72 hours resulting in a total flux of272×10⁻⁴ grams/hr-11 cm².

A liquid sweep stream of ethylene glycol was utilized in the liquid toliquid separation system; however the final sump was comprised of 80% byweight ethanol and 20% by weight water. The system had a separationfactor for water over ethanol of 2.0 and is not according to theinvention due to the membrane swelling caused by the high concentrationof ethanol in the feedstream.

The example was repeated utilizing the same membranes (4 mils vs. 3 milsthickness) and a feedstream comprised of 10% by weight ethanol and 90%by weight water for a period of 93 hours. A rate of 36×10⁻⁴ gram/hr-11cm² was achieved resulting in a final sump concentration of 25% byweight ethanol and 75% by weight water; thus the system was inaccordance with the invention having a separation factor for watercompared to ethanol of 0.25. No visible swelling of the membrane wasobserved as in the prior case.

EXAMPLES 16-20

Neutral organic components were removed from aqueous solutions utilizingmembranes which are selectively permeable to the organics under liquidto gas separation conditions. The following Table 2 presents the resultsachieved according to specific embodiments of the invention includingseparation of acrylonitrile from the aqueous solution throughfluorinated olefinic polymeric membranes. These fluorinated olefinicpolymeric membranes include copolymers as well as blends. Examples 16-20utilize in combination with the hydrophobic, fluorinated olefinicpolymeric membranes, a chemical potential gradient resulting frompervaporization conditions. Conditions such as concentration,temperature, rate, and separation factors for the various membranes andneutral organic component-aqueous solutions are presented in thefollowing Table 2.

                                      TABLE 2                                     __________________________________________________________________________    Pervaporization (1 atmosphere pressure on feed side and <0.1 mm Hg on the     permeate side)                                                                                                     Membrane                                                                            Separation                         Example               Temperature                                                                          Rate (grams/hr                                                                        thickness                                                                           Factor                             Number                                                                             Membrane  Feed   °C.                                                                           -11 cm.sup.2)                                                                         (mils)                                                                              (water/organic)                    __________________________________________________________________________    16   Blend 90% by wt                                                                         5% by wt                                                            poly (vinylidene                                                                        acrylonitrile                                                       fluoride) 10% by                                                                        0.1% by wt                                                          wt poly (vinyl-                                                                         acetonitrile                                                                         50     0.150   1     0.18                                    pyrrolidone)                                                                            0.002% by wt                                                                  propionitrile                                                  17   Copoly (ethylene/                                                                       5% by wt                                                            tetrafluoro-                                                                            acrylonitrile                                                       ethylene) (45/55                                                                        0.1% by wt                                                          molar ratio)                                                                            acetonitrile                                                                         50      0.0054 1     0.55                                              0.002% by wt                                                                  propionitrile                                                  18   Poly (vinylidene                                                              fluoride) 50% by wt                                                                     acetonitrile                                                                         50     0.453   1      0.300                             19   Poly (vinyl-                                                                            50% by wt                                                           fluoride) acetonitrile                                                                         50     1.091   1      0.613                             20   Fluorinated                                                                             50% by wt                                                           ethylene/propylene                                                                      acetonitrile                                                                         50      0.0032 1     0.70                                    copolymer                                                                __________________________________________________________________________

EXAMPLES 21-30

Neutral organic components were removed from aqueous solutions utilizingmembranes which are selectively permeable to the organics under liquidto gas separation conditions. The following Table 3 presents the resultsachieved according to the specific embodiments of the inventionincluding separation of ethanol, butanol, acrylonitrile, andacetonitrile through polymeric silicones and copolymers thereof.Examples 21-30 utilize in combination with the hydrophobic polymericsilicone membranes, a chemical potential gradient resulting frompervaporization conditions. Conditions such as concentration,temperature, rate, separation factor for the various membranes andneutral organic components are presented in the following Table 3.

                                      TABLE 3                                     __________________________________________________________________________    Pervaporization (1 atmosphere pressure on feed side and <0.1 mm Hg on         permeate side                                                                                                     Membrane                                  Example              Temperature                                                                          Rate (grams/hr                                                                        thickness                                                                           Factor                              Number                                                                             Membrane Feed   °C.                                                                           -11 cm.sup.2)                                                                         (mils)                                                                              (water/organic)                     __________________________________________________________________________    21   Silicone/poly-                                                                         50% by wt                                                            carbonate block                                                                        methanol                                                                             25     0.16    1     .218                                     copolymer                                                                22   Methylsilicone/                                                                        50% by wt                                                            phenylsilicone                                                                         methanol                                                                             60     0.016   17    0.80                                     copolymer                                                                23   Methylsilicone                                                                         50% by wt                                                            polymer  methanol                                                                             25     0.19    10    0.094                               24   Methylsilicone                                                                         50% by wt                                                            polymer  ethanol                                                                              25     0.16    10    0.20                                25   Dow silastic RTV                                                                       50% by wt                                                            585      ethanol                                                                              25     0.09    4     0.10                                26   Silicone/poly-                                                                         7% by wt                                                             carbonate block                                                                        butanol                                                                              25     0.085   1     0.066                                    copolymer                                                                27   Methylsilicone/                                                                        7% by wt                                                             phenylsilicone                                                                         butanol                                                                              60     0.0167  17    0.211                                    copolymer                                                                28   Methylsilicone                                                                         7% by wt                                                             polymer  butanol                                                                              25     0.11    10    0.049                               29   Methylsilicone                                                                         5% by wt                                                             polymer  acrylonitrile                                                                 0.1% by wt                                                                    acetonitrile                                                                         50     0.11    10    0.029                                             0.002% by wt                                                                  propionitrile                                                   30   Methylsilicone                                                                         50% by wt                                                            polymer  acetonitrile                                                                         50     0.25    15    0.095                               __________________________________________________________________________

EXAMPLE 31

A neutral organic component (ethanol) was removed from aqueous solutioncomprised of 90% ethanol and 10% water by weight utilizing a methylsilicone resin having a thickness of 13 mils. A rate of 670 grams/hr-11cm² ×10⁻⁴ was achieved at a temperature of 23° C. utilizing ethyleneglycol as a solution sweep fluid. The aqueous solution feedstream wascontacted with membrane for a period of 22 hours and resulted in a sumpcontent of 92% by weight ethanol vs. 8% by weight water in addition tothe ethylene glycol. The system separation factor for water over ethanolwas 0.26. The process was repeated utilizing a 10% by weight ethanol and90% by weight water aqueous solution feedstream with the results of arate of 260×10⁻⁴ gram/hr-11 cm² and a separation factor for water overethanol of 0.10. The content of the ethylene glycol included 43% byweight ethanol and 57% by weight water in addition to the ethyleneglycol.

EXAMPLE 32

A neutral organic component (ethanol) was removed from aqueous solutionwherein the solution was commprised of 90% by weight ethanol and 10% byweight water at 22° C. by contacting said solution with a Dow-Corningsilicone product (RTV 585 Silastic) (18 mils thick). The separationsystem resulted in a rate of 420×10⁻⁴ gram/hr-11 cm². Ethylene glycolwas utilized as a solution sink and the separation factor for water overethanol was 0.44.

The process was repeated utilizing an aqueous solution feedstreamcomprised of 10% by weight ethanol and 90% by weight water whichresulted in a rate of 50×10⁻⁴ gram/hr-11 cm² and a separation factor forwater over ethanol of 0.05. The solution sink was comprised of 49% byweight ethanol and 51% by weight water in addition to the ethyleneglycol. The total time for both separation procedures was 22 hrs.

EXAMPLE 33

A neutral organic component (ethanol) was removed from an aqueoussolution feedstream comprised of 10% by weight ethanol and 90% by weightwater through utilization of a methyl silicone resin having a thicknessof about 13 mils at a temperature of 25° C. A sweep fluid comprised ofmeta-xylene was utilized resulting in a sump concentration of 91% byweight ethanol and 9% by weight water in addition to the meta-xylene.The system achieved a separation factor for water over ethanol of lessthan 0.01.

EXAMPLE 34

An aqueous solution feedstream comprised of 5.3% acrylonitrile, 0.1%acetonitrile and 0.002% by weight propionitrile was contacted with aurethene member having a thickness of 1 mil under pervaporizationconditions of 50° C. The permeate side had less than 0.1 millimetersmercury vaccum condition with the separation resulting in a rate of0.156 grams/hour-11 cm² and a separation factor for water overacrylonitrile of 0.071.

EXAMPLE 35

According to the invention aliphatic nylon 66 and aliphatic nylon 12were utilized to separate butanol from water under pervaporizationconditions. However, ethanol, methanol, acrylonitrile and acetonitrilewere not selectively separated through these membranes from water. As aresult of these successes and failures it was analyzed that neutralorganic components having at least about 4 carbon atoms per moleculecould be utilized as an aqueous solution feedstream which would besuccessfully separated according to the invention through aliphaticnylons.

An aqueous feedstream comprised of 7% by weight butanol was contactedwith nylon 66 at 25° C. resulting in a rate of 0.087 gram/hr-11 cm² anda separation factor for water over butanol of 0.73. The same feedstreamwas contacted with nylon 12 at 75° C. resulting in a rate of 0.026gram/hr-11 cm² and a separation factor for water over butanol of 0.13.

What is claimed is:
 1. A process for separating neutral organics from anaqueous solution which comprises contacting an aqueous solutioncontaining neutral organics having at least four carbon atoms permolecule selected from alkanols, organic nitriles and alkyl benzeneswith a first surface of a hydrophobic polymeric membrane selected frompolysilicones and polyurethanes selectively permeable to the neutralorganic components contained in the aqueous solution; maintaining asecond and opposite membrane surface at a lower chemical potential thanthe first membrane surface for the neutral organic components;permeating a portion of said neutral organic components into and throughthe membrane; and withdrawing at the second membrane surface a mixturehaving a higher total concentration of the neutral organic componentsthan the total concentration of said neutral organic components in theaqueous solution contacting said first surface.
 2. The process of claim1 characterized in that both the aqueous solution permeant and thepermeate mixture are in the vapor phase.
 3. The process of claim 1wherein the lower chemical potential is maintained on the secondmembrane surface by contacting the second membrane surface with aneutral organics solution sink.
 4. The process of claim 1 or 3 whereinthe neutral organics are alkanols.
 5. The process of claim 4 wherein theneutral organics are butanol.
 6. The process of claim 1 or 3 wherein theneutral organics are organic nitriles.
 7. The process of claim 1 or 3wherein the neutral organics are alkylbenzenes.
 8. The process of claim1 wherein the neutral organics mixture withdrawn from the secondmembrane surface is in the vapor phase.
 9. The process of claim 1wherein the neutral organics mixture withdrawn from the second membranesurface is in the liquid phase.